SSI -- Server Side Includes

This approach was first used in HTTPD server (from NCSA), and then incorporated into Apache. Now, it is a de facto standard and present in many commercial Web servers. How it works?

• File needs to have special extension. Usually .shtml is used.
• Files with the .shtml are processed through a filter which looks for HTML comments <!--#somekeyword... --> with a special syntax.
• The special comment is replaced with dynamic content.

There are many SSI types. The popular SSIs are:

• <!--#include file="somefile" --> replaces tag with a file.
• <!--#set var="script_dir" value="/usr/local/bin" --> sets an environment variable (so the next call to a script can use it
• <!--#exec cgi="/cgi-bin/list_directory.pl" --> executes a CGI script
• <!--#exec cmd="ps -ef | grep nobody" --> executes a system commad (here it lists processes run by user nobody

Detailed syntax of SSI is avaliable from Apache Web site: http://httpd.apache.org/